This invention relates to low-pressure mercury-vapor discharge lamps, and in particular, those used for phototherapeutic treatment of infantile hyperbilirubinemia, which is a condition occurring in newborn infants where bilirubin is present in high concentrations such that there is significant red cell destruction.
A method of treating hyperbilirubinemia is disclosed in U.S. Pat. No. 3,658,068 dated Apr. 25, 1972 issued to J. W. McNall and assigned to the present assignee. This patent discloses that a lamp combination comprising a low-pressure mercury-vapor discharge device incorporating a phosphor of alkaline-earth metal halophosphate activated by divalent europium is particularly useful in the treatment of hyperbilirubinemia. This patent shows that utilizing the lamp combination described is effective in the treatment of hyperbilirubinemia because of concentration of the radiated energy in a portion of the spectrum which causes decomposition of the bilirubin constituent. The alkaline-earth metal halophosphate phosphors are highly absorptive of ultraviolet radiant energy, which energy is converted and re-emitted as a narrow band blue emission. The patent teaches that Sr.sub.3 (PO.sub.4).sub.3 Cl:Eu.sup.++ wherein the gram-atom ratio of europium to europium plus strontium is about 0.015 is the preferable composition from the standpoint of best efficiency of emission.
The foregoing patent gives an example of the treatment process in which about ten 20 watt lamps incorporating the blue-emitting phosphor are disposed in a unitary fixture which has an ultraviolet absorptive cover to prevent any possible exposure of the infant to ultraviolet radiation. The eyes of the infant to be treated are covered with a suitable light shield. The infant is disposed a distance from the fixture such that the energy level at the peak wavelength reaching the infant is about 90 microwatts per square centimeter per nanometer.
An alternative apparatus for phototherapeutic treatment of hyperbilirubinemia is disclosed in U.S. Pat. No. 3,822,706 dated July 9, 1974, issued to Simone et al. The Simone patent discloses a light comprising a neon bulb, which emits light radiation in the blue portion of the visible spectrum and having a filter means for absorption of ultraviolet radiation before transmission of the light to the infant. The neon light is mounted on a housing open at one end for permitting the head of the infant to extend outside of the housing. A shield is mounted on one end of the housing for shielding the infant's head from the light emitted from the neon lamp.
It has been found that occasionally, certain attendant individuals, such as the nurses, may experience a feeling of nausea, apparently as a result of continuously viewing the blue radiation emitted by a lamp operating at the optimum portion of the spectrum for phototherapeutic treatment of hyperbilirubinemia. Apparently, this is a visual phenomenon.